Don't check array bounds if we have been told not to.

Fixes range.go test for 6g.

R=rsc
CC=golang-dev
https://golang.org/cl/189093

src/cmd/5g/cgen.c

@@ -571,7 +571,7 @@ agen(Node *n, Node *res)
 				n1.xoffset = Array_array;
 				gmove(&n1, &n3);
 			} else
-			if(!debug['B']) {
+			if(!debug['B'] && !n->etype) {
 				if(v < 0)
 					yyerror("out of bounds on array");
 				else

src/cmd/6g/cgen.c

@@ -522,7 +522,7 @@ agen(Node *n, Node *res)
 				n1.xoffset = Array_array;
 				gmove(&n1, &n3);
 			} else
-			if(!debug['B']) {
+			if(!debug['B'] && !n->etype) {
 				if(v < 0)
 					yyerror("out of bounds on array");
 				else